The present patent application claims the right of priority under 35 U.S.C. xc2xa7119(a)-(d) of German Patent Application No. 100 25 321.0, filed May 22, 2000.
The present invention relates to multilayer film laminates, which are particularly impermeable to gas diffusion, and to the use of these gas diffusion impermeable multilayer film laminates in the production of vacuum insulation panels.
In some specific industrial products, such as for example in the production of vacuum insulation panels (VIP), there is a requirement for films which have extremely low gas diffusion values, in order to ensure that, once applied, the vacuum and thus the effectiveness of the VIPs are retained over a very long period of time (e.g., 10-15 years).
Conventional barrier layer films made from plastics, as described for example in EP-A 0 517 026, do not achieve the necessary gas barrier action. While composites which contain aluminum foil can provide a complete gas barrier, they are undesirable in many applications due to the thermal conductivity of the aluminum. Metallised films or films with a vapor deposited SiOx coating are furthermore known which avoid the disadvantages with regard to the thermal conductivity of pure metal foils (for example, as described in EP-A 0 878 298) and simultaneously achieve higher levels of barrier action than do pure plastics films. However, the levels of barrier action obtained with films having vapor deposited SiOx coatings are still far below the required gas barrier values.
As used herein and in the claims, the term xe2x80x9cvacuum insulation panels (VIPs)xe2x80x9d means sheet-like structures which include an insulating material or packing, that are vacuum packed in a high barrier film envelope. The level of the vacuum are here determined by the insulating material or packing used and the required insulation action of the VIP. Over the service life of the VIP, the high barrier film prevents the diffusion of gases which impair the vacuum and thus the insulating properties of the VIP. Metal foils are undesirable as high barrier films as they conduct heat around the edges of the sheet-form VIP, so reducing insulation performance.
The object of the present invention is accordingly to provide film laminates which achieve particularly elevated gas barrier action without using thermally conductive metal foils as a component. It is simultaneously intended to have a positive influence upon further mechanical and thermal properties of the film laminate by means of a suitable combination of materials. In particular, the intention is to provide film laminates which are suitable for the production of vacuum insulation panels (VIP).
In accordance with the present invention, there is provided a multilayer film laminate comprising at least three layers having the following sequence:
(I) at least two first plastic layers (e.g., (Ia), (Ib), (Ic), etc.), each of said first layers (I) having, on one side only, a vapor deposited coating selected independently from the group consisting of aluminum, SiOx and a metal oxide of main group 2 or 3 of the periodic table of the elements; and
(II) an exterior polyolefin heat sealing layer.
As used herein and in the claims, the term xe2x80x9cSiOxxe2x80x9d means silicon oxide, having x oxygen atoms, e.g., from 2 to n oxygen atoms.
As used herein and in the claims, the phrase xe2x80x9cmain group 2 or 3 of the periodic table of the elementsxe2x80x9d is meant to be inclusive of the elements Be, Mg, Ca, Sr, Ba, Al, Ga, In, Tl.
Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, etc. used in the specification and claims are to be under stood as modified in all instance by the term xe2x80x9cabout.xe2x80x9d
The initial expectation in this connection would be that gas barrier action is determined by the gas barrier action of the best of the individual layers or is calculated as the sum of the barrier actions of the individual layers, but, surprisingly, levels of gas barrier action are obtained which are not only distinctly higher than those of the individual layers but are in part distinctly higher than the sum of the individual layers. While not intending to be bound by any theory, this may, for example, be explained by supplementary (synergistic) coverage of defects in the individual vacuum deposit coated layers.
The vapor deposited coatings of each first film layer (I) of the multilayer film laminate of the present invention may be applied by art recognized methods.
In order to achieve still higher gas diffusion barrier values, further layers may be inserted or interposed between the layers of the multilayer film laminate of the present invention, e.g., between (Ia) and (Ib) and/or between (Ib) and (II). These additional layers may: (1) have, on one side only, a vapor deposited coating selected from aluminum, SiOx and a metal oxide of main group 2 or 3 of the periodic table of the elements; or (2) be free of a vapor deposited coating, while still having specific barrier properties, e.g., a layer of polyvinyl alcohol (PVOH) free of a vapor deposited coating.
The polymers of the layers of the multilayer film laminate of the present invention having a vapor deposited coating selected from aluminum, SiOx and a metal oxide of main group 2 or 3 may include any of the known conventional plastics, preferred examples of which include, but are not limited to polyesters, polyamides, polyolefins or the copolymers thereof. These layers having vapor deposited coatings may furthermore also be composed of coextruded plies of different polymers. The thickness of the individual layers is not essential in this connection, but will, to a small extent, influence gas barrier action and, furthermore, contribute to the mechanical and thermal properties of the multilayer film laminate of the present invention.
With the multilayer film laminates according to the invention, it is in particular possible to achieve oxygen diffusion values of less than 0.01 cm3/m2 d bar (determined at a temperature of 23xc2x0 C., and at 75% relative humidity) and water vapor diffusion values of less than 0.1 g/m2 d (determined at a temperature of 38xc2x0 C., and at 90% relative humidity). When the multilayer film laminates are produced with more than 3 layers, it is entirely possible also to obtain multilayer film laminates which achieve distinctly lower gas diffusion values still. By means of the combination of the various plies, it is not only possible to adjust the gas diffusion values to the values required by the application, but it is also possible to vary the mechanical and/or thermal characteristics of the resultant multilayer film laminate according to the invention by modifying the layer material which is provided with a vapor deposited coating selected from aluminium, SiOx and a metal oxide of main group 2 or 3.
If one of the first layers (I) is an external polyamide layer, e.g., an external polyamide layer (Ia), with a vapor deposited coating on one side of aluminum or SiOx or a metal oxide of main group 2 or 3, the resultant multilayer film laminate is distinguished, in addition to the good gas diffusion barrier values, by elevated mechanical stability, and in particular by elevated puncture resistance, which offers advantages in handling the multilayer film laminates according to the invention, so preventing damage to the laminates and VIPs produced therefrom. Such VIPs typically must at times withstand considerable mechanical loads both during manufacture and during installation in the final application, which may result in damage to the film and thus impaired barrier properties.
In an embodiment of the present invention, one of the first layers (I) is an external polypropylene layer, e.g., an external polypropylene layer (Ia), with a vapor deposited coating on one side of aluminum or SiOx or a metal oxide of group 2 or 3, which is distinguished by particularly good water vapor barrier action. If this external layer is then combined with a subsequent layer (Ib), which is composed of a polyester with a vapor deposited coating on one side of aluminum or SiOx or a metal oxide of main group 2 or 3, which is in turn distinguished by particularly good oxygen barrier action, the resultant multilayer film laminate according to the invention will be distinguished both by better water vapor barrier action in comparison with the polypropylene layer alone, and by better oxygen barrier action in comparison with the polyester layer alone. The crucial barrier elements of the combined external polypropylene layer (Ia) and polyester layer (Ib) not only complement but synergistically support each other in a particularly convincing manner.
In another embodiment of the present invention, at least one of the layers with a vapor deposited coating of aluminium or SiOx or a metal oxide of main group 2 or 3 is a coextruded layer, in which the coextruded layer is produced from at least one ply of polyamide (a), and at least one gas barrier ply (b). One particularly desirable structure is a 3-ply combination of polyamide in the outer layers and a copolymer of ethylene/vinyl alcohol (EVOH) as a gas barrier layer in the inner ply interposed between two polyamide plies. In the resultant multilayer film laminate according to the invention, the gas barrier ply provides extremely improved gas barrier values, in particular improved oxygen barrier values when EVOH is used as the gas barrier ply.
In a particularly preferred embodiment of the multilayer film laminate of the present invention, two of the layers with a vapor deposited coating of aluminium or SiOx or a metal oxide of main group 2 or 3 are laminated together with the vapor deposited layers against or abutting each other (e.g., abutting each other directly, or each abutting a common adhesive layer interposed there-between). While not intending to be bound by any theory, it is believed that this provides particularly advantageous gas barrier values as the two abutting vapor deposited coatings directly complement each other, such that microscopic damage in one vapor deposited coating may be covered by the second vapor deposited coating, giving rise to a disproportionate increase in barrier properties.
In one particularly preferred structure, at least one of the first layers (I), e.g., at least one of layers (Ia), (Ib), (Ic), etc., is provided with a vapor deposited coating of aluminium, preferably having a thickness of 30 to 80 nm.
Polyolefin homo- or polyolefin copolymers may be used as the heat sealing layer (II). Examples of polyolefin homo- or polyolefin copolymers that may be used as the heat sealing layer (II) include, but are not limited. to: linear low density polyethylene (LLDPE); polybutylene (PB); ethylene/vinyl acetate (EVA); polypropylene (PP); high density polyethylene (HDPE); ionomer polymers (IO); and mixtures of these substances are preferred. Amorphous polyethylene terephthalate (aPET) or other heat sealable polymer materials may also be used as the heat sealable layer (II). A multilayer embodiment of the heat sealing layer (II) produced by coextruding two or more layers of the stated materials is also possible according to the invention. The thickness of the heat sealing layer (II) is preferably 20 to 200 xcexcm, and particularly preferably 50 to 100 xcexcm.
In particular, ionomer sealing layers or other easy flowing sealing layers, which give rise to particularly gas tight seams under the dusty conditions typical in VIP production, are preferably used as the heat sealing layer (II) when the multilayer film laminates of the present invention are used in the production of VIPs.
Conventional commercially available reactive adhesives, such as and in particular two component polyurethane adhesives, may be used as the adhesive and bonding layer between the individual layers of the multilayer film laminates of the present invention. It is, however, also possible to use polyolefin coupling agents, preferably polyethylene homopolymer, ethylene/ethyl acrylate (EEA) or ethylene/methacrylic acid (EMA) as an adhesive or bonding layer between the individual layers of the multilayer film laminate. However, the multilayer film laminate according to the invention, and in particular the gas barrier action thereof, does not essentially depend upon the nature of the bond between the individual layers.
When two component polyurethane adhesives are used as an adhesive bonding agent or layer between the individual layers of the multilayer film laminates of the present invention, care must typically be taken to ensure that the components of the two component polyurethane adhesives are selected such that a minimum evolution of gas occurs during the bonding process. Otherwise, gas bubbles may, undesirably, form in the bonding layers.